Schema; `exworkflows` does nothing

[MetRonnie]

https://github.com/cylc/cylc-uiserver/blob/aeddbcb01ca68de01258ccdd1c129614361fdde9/cylc/uiserver/schema.py#L287-L297

exworkflows is a list of workflows to exclude. However we are not doing any filtering here based on the value of exworkflows.

E.g. see the workflow_filter function in https://github.com/cylc/cylc-flow/blob/0e5fa06a7267772d94024761ca9ac20b6b11339c/cylc/flow/network/resolvers.py#L178

[oliver-sanders]

Note, we aren't actually using this and don't have a use case in mind for it in the future.